Parashas Behar · Aliyah 4 · Passuk 25:27
Chabad.org — English translation + Rashi
Torah Temimah cites Sifra (Torat Kohanim).
English: “And he shall return the surplus.” This teaches that he returns the remainder.
Classical derasha (Sifra).
The buyer receives back the unused portion of the purchase price corresponding to the years he will not enjoy.